In recent years, with the spread of the Internet, electronic mails have become indispensable as a tool for business communication between companies.
However, when a person belonging to a company sends an electronic mail intended for another company, there may be cases where the electronic mail is inadvertently sent to a wrong destination because of a human factor (error), and important information such as company's know-how or personal information described in a mail text or an attached file is leaked to a third party. This may possibly lead to a serious incident related to the survival of the company.
To avoid inconvenience due to such erroneous transmission of electronic mails, there has been proposed a technique (hereinafter referred to as a publicly known technique 1) which provides a checkbox corresponding to a mail address of a transmission destination, and makes a sender (addresser) check that the mail address is correct, and then allows the transmission of the electronic mail (for example, see Patent Literatures 1, 2).